This invention relates to an ignition timing control system for an internal combustion engine such as an outboard engine, and in particular to an ignition timing control apparatus which improves the decceleration, starting acceleration, and idling stability of the engine.
In outboard motors, etc., the ignition timing of the engine during starting is set at 5.degree. Before Top Dead Center (hereinafter abbreviated as BTDC) to ensure starting, and during idling the ignition timing is set at 5.degree. After Top Dead Center (hereinafter abbreviated as ATDC) to stabilize the revolutions of the engine at low engine speeds. When accelerating the throttle valve of the engine is opened while at the same time the ignition timing is advanced to 25.degree.-30.degree. BTDC to enhance the acceleration. However, since it is extremely complicated to provide the above operations by means of an automatic advance angle mechanism, a typical ignition timing control apparatus has freely rotatably disposed therein the stator of an ignition signal generator which is interlocked with the throttle lever of the engine by means of a ball joint with the direction of the axis of the rotatable rotor being fixed, resulting in a relatively complicated structure. Therefore, in the case where the ignition signal generator is freely rotatably disposed, a mechanism portion mainly formed of a bearing portion, a sustaining member for fixing the stator in the axial direction, and the ball joint interconnected with the throttle lever are easily worn and may break due to the vibration of the engine.
While an ignition timing control apparatus with the ignition angle advanced corresponding to the engine speed according to the output of the ignition signal generator has also been used, the startability of the engine and the stability during idling in this apparatus have not been improved yet.
Furthermore, the ignition timing control apparatus disclosed in U.S. Pat. No. 4,244,336, uses a method of advancing the ignition angle in the shape of a mountain in the low speed region. However, this method is inferior in the startability and acceleration although stability during idling is good.
As other prior art, there have been proposed Japanese Utility Model Application Laid-open No. 58-180385 published on Dec. 2, 1983, entitled "Electronic Advance Angle Ignition Apparatus" by Hitachi Works Co., Ltd. which discloses advancing the ignition timing of an engine by changing the activation level of an ignition timing control circuit according to the condition of an idle switch; Japanese Utility Model Application Laid-open No. 56-27412 published on June 30, 1981, entitled "Contactless Ignition Apparatus" by Nippon Denso Co., Ltd. which discloses the provision of a switch turned on during high speed deceleration of the engine and retarding the ignition timing by shortcircuiting an advancing ignition signal when the switch is on; and, Japanese Patent Application Laid-open No. 58-65972 published on Apr. 19, 1983, entitled "Ignition Apparatus for internal Combustion Engine of Outboard Motor" by Hitachi Works Co., Ltd. which discloses the provision of a switch interlocked with the throttle valve of an engine and advancing the ignition timing when the opening of the throttle valve reaches a predetermined degree.